One cannot walk up to a range animal to administer an injection of medication, in the same fashion one can approach a domesticated farm animal. Ranchers have, therefore, developed specialized delivery systems to assist them in injecting medication into range animals. These delivery systems consist of pole mounted syringes or syringe bearing missiles that enable the rancher to reach a fast moving range animal from a distance. The syringes are connected to a pressure source that force the medication from the syringe upon the needle penetrating the hide of the animal.
Once the hide of the animal has been pierced by the needle on the syringe, the animal usually bolts. The rancher cannot hope to keep pace with the animal, and therefore must wait until the needle works its way out of the animal before retrieving his pole or missile. The normal operation of gravity results in the needle eventually working its way out of the hide of the animal. However, experience has shown that this can be extremely irritating to the animal. After the needle has fallen out as a result of gravity, the animal is obviously distressed and does not resume it normal activities for a considerable length of time. The animal makes a connection between the discomfort experienced and the presence of the rancher, making it even more difficult for the rancher to approach the animal in future.
In order to address this problem, retrieval systems have been employed in which a substantial length of string is attached to the pole or missile. The advantage of the string retrieval system is that the needle may be pulled out by means of the string as soon as the rancher is confident the medication has been administered. The animal suffers less distress and is able to resume its normal activities more rapidly. The animal is less likely to associate the temporary discomfort with the rancher. However, string retrieval systems have other disadvantages associated with them. The string gets dragged through manure and dirt in the pasture or feed lot, making it a messy solution. The string often gets caught, resulting in the needle being pulled out prematurely. There are a multitude of ways in which the string can get caught. For example, it can become wrapped in the feet of other cattle, or around bushes as the animal weaves back and forth after having bolted at the time of the injection. Unless a substantial length of string is employed, a fast moving animal can reach the end of the string, resulting in the needle being pulled out before the full dosage of medication has been administered. However, the longer the length of string employed the more tangles the rancher must deal with before he is in a position to use the delivery system to administer another injection. Even if all else goes well, there is always a danger that when the rancher pulls the string, the needle will comes flying back at him.